Semicoductor wafer and method of backside probe testing through opening in film frame

ABSTRACT

A semiconductor test system has a film frame including a tape portion with one or more openings through the tape portion. The opening is disposed in a center region of the tape portion of the film frame. The film frame may have conductive traces formed on or through the tape portion. A thin semiconductor wafer includes a conductive layer formed over a surface of the semiconductor wafer. The semiconductor wafer is mounted over the opening in the tape portion of the film frame. A wafer probe chuck includes a lower surface and raised surface. The film frame is mounted to the wafer probe chuck with the raised surface extending through the opening in the tape portion to contact the conductive layer of the semiconductor wafer. The semiconductor wafer is probe tested through the opening in the tape portion of the film frame.

CLAIM TO DOMESTIC PRIORITY

The present application is a continuation of U.S. patent applicationSer. No. 15/704,246 to Michael Seddon et al., filed Sep. 14, 2017, nowpending, which is a continuation of U.S. patent application Ser. No.15/230,875, filed Aug. 8, 2016, now U.S. Pat. No. 9,793,186 issued onOct. 17, 2017, the entirety of each of which are herein incorporated byreference.

TECHNICAL FIELD

The present disclosure relates in general to semiconductor devices and,more particularly, to a semiconductor wafer and method of probe testingfrom a backside of the wafer through one or more openings in a tapeportion of a film frame.

BACKGROUND

Semiconductor devices are commonly found in modern electronic products.Semiconductor devices vary in the number and density of electricalcomponents. Semiconductor devices perform a wide range of functions suchas analog and digital signal processing, sensors, transmitting andreceiving electromagnetic signals, controlling electronic devices, powermanagement, and audio/video signal processing. Discrete semiconductordevices generally contain one type of electrical component, e.g., lightemitting diode (LED), small signal transistor, resistor, capacitor,inductor, diodes, rectifiers, thyristors, and powermetal-oxide-semiconductor field-effect transistor (MOSFET). Integratedsemiconductor devices typically contain hundreds to millions ofelectrical components. Examples of integrated semiconductor devicesinclude microcontrollers, application specific integrated circuits(ASIC), power conversion, standard logic, amplifiers, clock management,memory, interface circuits, and other signal processing circuits.

A semiconductor wafer includes a base substrate material and pluralityof semiconductor die formed on an active surface of the wafer separatedby a saw street. Many applications require the semiconductor die to bereduced in height or thickness to minimize the size of the semiconductorpackage. Testing and inspection of the semiconductor wafer is importantfor quality assurance and reliability. Testing typically involvescontacting a surface of the semiconductor wafer with a test probe. Yet,for large thin semiconductor wafers, wafer test probing often leads tobreakage or damage from probe pressure on the thin wafer surface, aswell as wafer handling and wafer warpage. The thin semiconductor wafersare subject to warpage. A warped thin semiconductor wafer is difficultto test because the test probes may not make contact with the warpedsurface.

In some cases, wafer test probing is performed prior to wafer thinningbecause the large thin wafers, e.g., wafers with a diameter of 150-300millimeters (mm), may be warped beyond the test probe contact tolerance,or because the thin wafer surface cannot handle the invasive nature ofthe test. Wafer testing prior to wafer thinning is incomplete becausecertain features that are added post-wafer thinning, e.g., back-sidemetal, are not present for the test. In addition, for MOSFETS or waferswith through silicon vias, the current flows through the silicon and outthe backside of the thinned wafer, i.e. through the back metal. Testingsuch devices is impractical for full-thickness wafers. The thickness ofthe wafers also affects the electrical performance. A thicker T-MOSFETwafer has more resistance than a thin wafer since the current must passthrough more silicon. Wafer testing and inspection before all featuresare present reduces quality assurance, and adds manufacturing costbecause an untested die must be assembled before functionality can beconfirmed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1b illustrate a semiconductor wafer with a plurality ofsemiconductor die separated by a saw street;

FIGS. 2a-2h illustrate a process of thinning a semiconductor wafer withan edge support ring; and

FIGS. 3a-3m illustrate a process of probe testing from a backside of thethinned semiconductor wafer through one or more openings in a tapeportion of a film frame.

DETAILED DESCRIPTION OF THE DRAWINGS

The following describes one or more embodiments with reference to thefigures, in which like numerals represent the same or similar elements.While the figures are described in terms of the best mode for achievingcertain objectives, the description is intended to cover alternatives,modifications, and equivalents as may be included within the spirit andscope of the disclosure. The term “semiconductor die” as used hereinrefers to both the singular and plural form of the words, andaccordingly, can refer to both a single semiconductor device andmultiple semiconductor devices.

Semiconductor devices are generally manufactured using two complexmanufacturing processes: front-end manufacturing and back-endmanufacturing. Front-end manufacturing involves the formation of aplurality of die on the surface of a semiconductor wafer. Each die onthe wafer may contain active and passive electrical components andoptical devices, which are electrically connected to form functionalelectrical circuits. Active electrical components, such as transistorsand diodes, have the ability to control the flow of electrical current.Passive electrical components, such as capacitors, inductors, andresistors, create a relationship between voltage and current necessaryto perform electrical circuit functions. The optical device detects andrecords an image by converting the variable attenuation of light wavesor electromagnetic radiation into electric signals.

Back-end manufacturing refers to cutting or singulating the finishedwafer into the individual semiconductor die and packaging thesemiconductor die for structural support, electrical interconnect, andenvironmental isolation. The wafer is singulated using plasma etching,laser cutting tool, or saw blade along non-functional regions of thewafer called saw streets or scribes. After singulation, the individualsemiconductor die are mounted to a package substrate that includes pinsor interconnect pads for interconnection with other system components.Interconnect pads formed over the semiconductor die are then connectedto interconnect pads within the package. The electrical connections canbe made with conductive layers, bumps, stud bumps, conductive paste, orwirebonds. An encapsulant or other molding material is deposited overthe package to provide physical support and electrical isolation. Thefinished package is then inserted into an electrical system and thefunctionality of the semiconductor device is made available to the othersystem components.

FIG. 1a shows a semiconductor wafer 100 with a base substrate material102, such as silicon, germanium, aluminum phosphide, aluminum arsenide,gallium arsenide, gallium nitride, indium phosphide, silicon carbide, orother bulk semiconductor material. A plurality of semiconductor die 104is formed on wafer 100 separated by saw street 106, as described above.Saw street 106 provides singulation areas to separate semiconductorwafer 100 into individual semiconductor die 104. In one embodiment,semiconductor wafer 100 has a width or diameter of 100-450 mm andthickness of 675-775 micrometers (μm). In another embodiment,semiconductor wafer 100 has a width or diameter of 150-300 mm.

FIG. 1b shows a cross-sectional view of a portion of semiconductor wafer100. Each semiconductor die 104 has a back surface 108 and an activesurface or region 110 containing analog or digital circuits implementedas active devices, passive devices, conductive layers, and dielectriclayers formed within the die and electrically interconnected accordingto the electrical design and function of the die. For example, thecircuit may include one or more transistors, diodes, and other circuitelements formed within active surface or region 110 to implement analogcircuits or digital circuits, such as digital signal processor (DSP),microcontrollers, ASIC, power conversion, standard logic, amplifiers,clock management, memory, interface circuits, and other signalprocessing circuit. Semiconductor die 104 may also contain integratedpassive devices (IPDs), such as inductors, capacitors, and resistors,for RF signal processing. Active surface 110 may contain an image sensorarea implemented as semiconductor charge-coupled devices (CCD) andactive pixel sensors in complementary metal-oxide-semiconductor (CMOS)or N-type metal-oxide-semiconductor (NMOS) technologies. Alternatively,semiconductor die 104 can be an optical lens, detector, vertical cavitysurface emitting laser (VCSEL), waveguide, stacked die, electromagnetic(EM) filter, or multi-chip module.

An electrically conductive layer 112 is formed over active surface 110using PVD, CVD, electrolytic plating, electroless plating process,evaporation, or other suitable metal deposition process. Conductivelayer 112 includes one or more layers of aluminum (Al), copper (Cu), tin(Sn), nickel (Ni), gold (Au), silver (Ag), titanium (Ti), titaniumtungsten (TiW), or other suitable electrically conductive material.Conductive layer 112 operates as interconnect pads electricallyconnected to the circuits on active surface 110.

FIGS. 2a-2h illustrate a process of thinning a semiconductor wafer withan edge support ring. FIG. 2a shows an entire area of semiconductorwafer 100 with back surface 108 and active surface 110. Semiconductordie 104 are present in active surface 110, see FIGS. 1a -1 b, but notlabeled for purposes of the present explanation. Semiconductor wafer 100has a pre-grinding thickness T₁ of 675-775 μm.

In FIG. 2b , semiconductor wafer 100 is inverted and mounted with activesurface 110 oriented to backgrinding tape 120. In FIG. 2c , the entireback surface 108 undergoes a first backgrinding operation with grinderor grinding wheel 122 to remove a portion of base substrate material 102down to surface 124. Semiconductor wafer 100 has a post-grindingthickness T₂ of 355 μm between active surface 110 and surface 124.

In FIG. 2d , a second grinding operation is applied to surface 124 usinggrinder or grinding wheel 128. Grinding wheel 128 moves in a cyclic,rotating pattern across an interior region or wafer grinding area 130 ofsemiconductor wafer 100 to remove a portion of base substrate material102 down to surface 134. Grinding wheel 128 is controlled to leave edgesupport ring 136 of base substrate material 102 around a perimeter ofsemiconductor wafer 100 for structural support. In one embodiment, thepost-grinding thickness T₃ of semiconductor wafer 100 is 75 μm or less.In another embodiment, the post-grinding thickness T₃ of semiconductorwafer 100 is 10-50 μm.

FIG. 2e shows a top view of grinding wheel 128 removing a portion ofsurface 134 of semiconductor wafer 100 to reduce the thickness of thesemiconductor wafer, and correspondingly semiconductor die 104, ingrinding area 130, while leaving edge support ring 136 of base substratematerial 102 around a perimeter of the semiconductor wafer. Edge supportring 136 has a width W₁₃₆ of 3.0 mm±0.3 mm from inner wall 154 to outeredge 156 around semiconductor wafer 100. The height of edge support ring136 is the first post-grinding thickness T₂, which is greater than thesecond post-grinding thickness T₃ of semiconductor wafer 100, tomaintain structural integrity of the thinner semiconductor wafer.

In FIG. 2f , a post-grinding stress relief etch is used to remove orreduce the damage in surface 134 of base substrate material 102 causedby the grinding process. Surface 134 of semiconductor wafer 100 iscleaned with a rinsing solution. An electrically conductive layer 172 isformed over surface 134 using PVD, CVD, electrolytic plating,electroless plating process, evaporation, or other suitable metaldeposition process. Conductive layer 172 includes one or more layers ofAl, Cu, Sn, Ni, Au, Ag, Ti, TiW, or other suitable electricallyconductive material. Conductive layer 172 provides back-side electricalinterconnect for semiconductor die 104. Conductive layer 172 ispatterned into electrically common or electrically isolated portionsaccording to the function of semiconductor die 104. Backgrinding tape120 is removed by exposing the tape to ultraviolet (UV) light andpeeling off.

In FIG. 2g , the thinned semiconductor wafer 100 is mounted with activesurface 110 oriented to tape portion 176 of film frame or carrier 178.In FIG. 2h , edge support ring 136 is removed to be planar with or justabove (10-13 μm) conductive layer 172 or surface 134.

FIGS. 3a-3m illustrate a process of probe testing from a backside of thesemiconductor wafer through one or more openings in a tape portion of afilm frame. In FIG. 3a , the thinned semiconductor wafer 100 is removedfrom film frame 178 and positioned above film frame or carrier 180 withconductive layer 172 on surface 134 oriented toward the film frame.Semiconductor die 104 on the thinned semiconductor wafer 100 have a fullfeature set, i.e., all functional components and layers have beenformed, ready for probe testing of the final semiconductor die. Filmframe 180 includes a tape portion 182 and edge support 184. Inparticular, tape portion 182 includes an opening 186 extending through acenter region of the tape portion. The thinned semiconductor wafer 100is positioned over film frame 180 with conductive layer 172 aligned andcentered with opening 186. FIG. 3b shows a top view of film frame 180with tape portion 182 and opening 186 extending through a center regionof the tape portion. Semiconductor wafer 100 is mounted to tape portion182 of film frame 180 with conductive layer 172 disposed over opening186. FIG. 3c shows a top view of semiconductor wafer 100 mounted to tapeportion 182 of film frame 180. Conductive layer 172 is accessiblethrough opening 186 in tape portion 182.

In FIG. 3d , semiconductor wafer 100 and film frame 180 are positionedover surface 190 of wafer probing chuck 194. Surface 190 has a lowerportion 190 a and a raised portion 190 b. The raised portion 190 b isaligned with opening 186. FIG. 3e shows film frame 180 withsemiconductor wafer 100 mounted to surface 190 of wafer probing chuck194 with tape portion 182 contacting lower portion 190 a of surface 190,and raised portion 190 b extending through opening 186 to contactconductive layer 172. In one embodiment, wafer probing chuck 194 draws avacuum through ports 193 to hold tape portion 182 and semiconductorwafer 100 securely in place with surface 134 and a first portion ofconductive layer 172 held flat against and in contact with tape portion182, tape portion 182 held flat against and in contact with lowerportion 190 a of surface 190, and a second portion of conductive layer172 held flat against and in contact with raised portion 190 b ofsurface 190. In FIG. 3f , a porous ceramic chuck 194, with the samesurface 190 including lower portion 190 a and raised portion 190 b,evenly distributes the vacuum forces to hold semiconductor wafer 100 andfilm frame 180 flat against lower portion 190 a and raised portion 190 bof surface 190. Semiconductor wafer 100 and film frame 180 being heldflat against lower portion 190 a and raised portion 190 b of surface 190by vacuum ports 193 or porous chuck 194 keeps the wafer stable andplanar during probe testing. Alternatively, tape portion 182 andsemiconductor wafer 100 are held securely in place by a press-fit withforce F, as shown in FIG. 3g , with surface 134 and a first portion ofconductive layer 172 held flat against and in contact with tape portion182, tape portion 182 held flat against and in contact with lowerportion 190 a of surface 190 of chuck 195, and a second portion ofconductive layer 172 held flat against and in contact with raisedportion 190 b of surface 190. Chuck 195 has the same surface 190 withlower portion 190 a and raised portion 190 b.

Semiconductor wafer 100 undergoes electrical testing and inspection aspart of a quality control process. Manual visual inspection andautomated optical systems are used to perform inspections onsemiconductor wafer 100. Software can be used in the automated opticalanalysis of semiconductor wafer 100. Visual inspection methods mayemploy equipment such as a scanning electron microscope, high-intensityor ultra-violet light, metallurgical microscope, or optical microscope.Semiconductor wafer 100 is inspected for structural characteristicsincluding warpage, thickness variation, surface particulates,irregularities, cracks, delamination, contamination, and discoloration.

The active and passive components within semiconductor die 104 undergotesting at the wafer level for electrical performance and circuitfunction. Each semiconductor die 104 is tested for functionality andelectrical parameters. The raised portion 190 b of surface 190 of waferprobing chuck 194 makes electrical contact with conductive layer 172through opening 186. A computer controlled test system 196 sendselectrical test signals through wafer probing chuck 194 and raisedportion 190 b of surface 190, which extends through opening 186, toprovide electrical stimuli to conductive layer 172. Alternatively,computer controlled test system 196 sends electrical test signalsthrough conductive channels within wafer probing chuck 194 and raisedportion 190 b of surface 190 to provide electrical stimuli to conductivelayer 172. Conductive layer 172 is coupled to circuits on active surface110 through conductive vias or vertically formed semiconductor devices.Semiconductor die 104 responds to the electrical stimuli, which ismeasured by computer test system 196 and compared to an expectedresponse to test functionality of the semiconductor die.

The testing of semiconductor wafer 100 from the back-side directly toconductive layer 172 is achieved through raised portion 190 b of surface190 of wafer probing chuck 194 extending through opening 186 in tapeportion 182 of film frame 180. Many testing procedures can beaccomplished with wafer probe contact of raised portion 190 b toconductive layer 172. For example, the electrical tests may includecircuit functionality, lead integrity, resistivity, continuity,reliability, junction depth, ESD, RF performance, drive current,threshold current, leakage current, and operational parameters specificto the component type. The testing is conducted with the thinnedsemiconductor wafer 100 after wafer grinding. The thinned semiconductorwafer 100 remains flat and stable by nature of lower portion 190 a andraised portion 190 b of surface 190 of wafer probing chuck 194 heldagainst conductive layer 172. The inspection and electrical testing ofsemiconductor wafer 100, after wafer thinning, enables semiconductor die104, with a complete feature set that passes, to be designated as knowngood die for use in a semiconductor package.

Semiconductor wafer 100 can also be tested from active surface 110, asshown in FIG. 3h . Each semiconductor die 104 is tested forfunctionality and electrical parameters using a test probe head 200including a plurality of probes or test leads 202, or other testingdevice. Probes 202 are used to make electrical contact with nodes orconductive layer 112 on each semiconductor die 104 and provideelectrical stimuli to interconnect pads 112. Semiconductor die 104responds to the electrical stimuli, which is measured by computer testsystem 206 and compared to an expected response to test functionality ofthe semiconductor die. The electrical tests may include circuitfunctionality, lead integrity, resistivity, continuity, reliability,junction depth, ESD, RF performance, drive current, threshold current,leakage current, and operational parameters specific to the componenttype. The inspection and electrical testing of semiconductor wafer 100enables semiconductor die 104 that pass to be designated as known gooddie for use in a semiconductor package.

In another embodiment, the film frame may have multiple openings toprovide access to different areas of the conductive layer. As notedabove, conductive layer 172 is patterned into electrically common orelectrically isolated portions according to the function ofsemiconductor die 104. FIG. 3i shows a top view of film frame 210including tape portion 212, edge support 214, and multiple openings 216.Tape portion 212 has as many openings 216 as necessary to performtesting of requisite areas of conductive layer 172. In this case, waferprobing chuck 194 would have multiple raised portions 190 b aligned withopenings 216. FIG. 3j shows film frame 210 with semiconductor wafer 100mounted to surface 190 of wafer probing chuck 194 with tape portion 212contacting lower portion 190 a of surface 190 and multiple raisedportion 190 b extending through multiple openings 216 to contactdifferent areas of conductive layer 172. Tape portion 212 andsemiconductor wafer 100 are held securely in place by a press-fit orvacuum assist with surface 134 and first portions of conductive layer172 held flat against and in contact with tape portion 212, tape portion212 held flat against and in contact with lower portion 190 a of surface190, and second portions of conductive layer 172 held flat against andin contact with raised portion 190 b of surface 190. Semiconductor wafer100 and film frame 210 being held flat against lower portions 190 a andraised portions 190 b of surface 190 by press-fit or vacuum assist keepsthe wafer stable and planar during probe testing.

The multiple raised portions 190 b of surface 190 of wafer probing chuck194 make electrical contact with corresponding areas of conductive layer172 through openings 216. A computer controlled test system 220 sendselectrical test signals through wafer probing chuck 194 and raisedportions 190 b of surface 190, which extends through openings 216, toprovide electrical stimuli to different areas of conductive layer 172.Semiconductor die 104 responds to the electrical stimuli, which ismeasured by computer test system 220 and compared to an expectedresponse to test functionality of the semiconductor die.

In another embodiment, similar to FIGS. 3i -3 j, the film frame may havemultiple openings and conductive traces or channels formed in the tapeportion of the film frame to provide access to different areas of theconductive layer. FIG. 3k shows a top view of film frame 230 includingtape portion 232, edge support 234, and multiple openings 236.Conductive traces 238 formed on the surface of tape portion 232 orformed through the tape portion. Alternatively, tape portion 232 may bemade with channels of conductive carbon 240, as shown in FIG. 3 l. Tapeportion 232 has as many openings 236 and conductive traces 238 orchannels 240 as necessary to perform testing of requisite areas ofconductive layer 172. In another embodiment, any portion or the entiretape portion 232 may be conductive to perform testing of requisite areasof conductive layer 172. Tape portion 232 and semiconductor wafer 100are held securely in place by a press-fit or vacuum assist with surface134 and first portions of conductive layer 172 held flat against and incontact with tape portion 232, tape portion 232 held flat against and incontact with lower portion 190 a of surface 190, and second portions ofconductive layer 172 held flat against and in contact with raisedportion 190 b of surface 190. Semiconductor wafer 100 and film frame 230being held flat against lower portions 190 a and raised portions 190 bof surface 190 by press-fit or vacuum assist keeps the wafer stable andplanar during probe testing.

In FIG. 3m , the multiple raised portions 190 b of surface 190 of waferprobing chuck 194 make electrical contact with corresponding areas ofconductive layer 172 through openings 236 and conductive traces 238 orchannels 240. Computer controlled test system 244 sends electrical testsignals through wafer probing chuck 194 and raised portions 190 b ofsurface 190, which extends through openings 236, to provide electricalstimuli through conductive traces 238 or channels 240 to different areasof conductive layer 172. Semiconductor die 104 responds to theelectrical stimuli, which is measured by computer test system 244 andcompared to an expected response to test functionality of thesemiconductor die.

The film frame and semiconductor wafer 100 are moved from wafer probingchuck 194 and the thinned semiconductor wafer 100 is singulated throughsaw streets 106 using a saw blade or laser cutting tool or plasma etchinto individual semiconductor die 104. The individual semiconductor die104 from the thinned semiconductor wafer 100 have been probe tested inthe final configuration of the semiconductor die.

While one or more embodiments have been illustrated and described indetail, the skilled artisan will appreciate that modifications andadaptations to those embodiments may be made without departing from thescope of the present disclosure.

What is claimed:
 1. A method of making a semiconductor device,comprising: providing a semiconductor wafer including a first side and asecond side, wherein the first side comprises a plurality ofsemiconductor devices formed therein; forming a conductive layer overthe second side; providing a wafer holder; forming a first openingthrough the wafer holder; mounting the semiconductor wafer to the waferholder with the conductive layer on the second side oriented toward thewafer holder; and probe testing the semiconductor wafer by contactingthe conductive layer through the first opening in the wafer holder. 2.The method of claim 1, wherein the wafer holder includes a tape portionwith the first opening formed in the tape portion.
 3. The method ofclaim 1, further including: providing a wafer probe chuck including araised surface; and mounting the wafer holder to the wafer probe chuckwith the raised surface extending through the first opening in the waferholder.
 4. The method of claim 1, further including forming a pluralityof openings through the wafer holder.
 5. The method of claim 1, furtherincluding mounting the semiconductor wafer to the wafer holder afterforming the first opening through the wafer holder.
 6. The method ofclaim 1, further including forming the first opening through the waferholder after mounting the semiconductor wafer to the wafer holder.
 7. Amethod of making a semiconductor device, comprising: providing asemiconductor wafer comprising a first side and a second side oppositethe first side, wherein the first side comprises a plurality ofsemiconductor devices therein; providing a wafer holder; forming a firstopening through the wafer holder; mounting the semiconductor wafer tothe wafer holder with the second side of the semiconductor waferoriented toward the wafer holder; and probe testing the semiconductorwafer by contacting the second side of the semiconductor wafer throughthe first opening in the wafer holder.
 8. The method of claim 7, whereinthe wafer holder includes a tape portion with the first opening formedin the tape portion.
 9. The method of claim 7, further including:forming a conductive layer over the second side of the semiconductorwafer; and probe testing the semiconductor wafer by contacting theconductive layer through the first opening in the wafer holder.
 10. Themethod of claim 7, further including: providing a wafer probe chuckincluding a raised surface; and mounting the wafer holder to the waferprobe chuck with the raised surface extending through the first openingin the wafer holder.
 11. The method of claim 7, further includingforming a plurality of openings through the wafer holder.
 12. The methodof claim 7, further including mounting the semiconductor wafer to thewafer holder after forming the first opening through the wafer holder.13. The method of claim 7, further including forming the first openingthrough the wafer holder after mounting the semiconductor wafer to thewafer holder.
 14. An apparatus for probe testing a semiconductor wafercomprising a first side and a second side opposite the first side,wherein the first side comprises of plurality of semiconductor devicestherein, the apparatus comprising: a holder with a first opening formedthrough the wafer holder, wherein the second side of the semiconductorwafer is disposed over the first opening in the wafer holder to probetest the semiconductor wafer through the first opening in the waferholder by contacting the second side of the semiconductor wafer.
 15. Theapparatus of claim 14, wherein the wafer holder includes a tape portionwith the first opening formed in the tape portion.
 16. The apparatus ofclaim 14, further including a conductive layer formed over the secondside of the semiconductor wafer.
 17. The apparatus of claim 14, furtherincluding a wafer probe chuck including a raised surface, wherein thewafer holder is disposed over the wafer probe chuck with the raisedsurface extending through the first opening in the wafer holder.
 18. Theapparatus of claim 14, further including a plurality of openings formedthrough the wafer holder.
 19. The apparatus of claim 14, wherein athickness of the semiconductor wafer is less than 75 micrometers. 20.The apparatus of claim 14, further including a conductive trace formedin or on the wafer holder.